refactor(affiliate): tighten DI and harden inviter code validation

- Drop SetAffiliateService setters and ProvideAuthService /
  ProvidePaymentService / ProvideUserHandler wrappers in favor of direct
  Wire constructor injection. AffiliateService has no back-edge to
  Auth/Payment/User, so the indirection was never required.
- Change RegisterWithVerification's variadic affiliateCode to a fixed
  parameter; adjust all call sites.
- Validate aff_code length and charset in BindInviterByCode before any
  DB lookup, eliminating timing-side-channel and useless DB roundtrips
  on malformed input.
- Make affiliate cache invalidation synchronous; surface Redis errors
  via the project logger instead of swallowing them in a detached
  goroutine.
- Add an integration test guarding cross-layer tx propagation in
  AccrueQuota and a unit test pinning the aff_code format rules.

backend/internal/service/payment_service.go

@@ -184,19 +184,12 @@ type PaymentService struct {
 	affiliateService *AffiliateService
 }
 
-func NewPaymentService(entClient *dbent.Client, registry *payment.Registry, loadBalancer payment.LoadBalancer, redeemService *RedeemService, subscriptionSvc *SubscriptionService, configService *PaymentConfigService, userRepo UserRepository, groupRepo GroupRepository) *PaymentService {
-	svc := &PaymentService{entClient: entClient, registry: registry, loadBalancer: newVisibleMethodLoadBalancer(loadBalancer, configService), redeemService: redeemService, subscriptionSvc: subscriptionSvc, configService: configService, userRepo: userRepo, groupRepo: groupRepo}
+func NewPaymentService(entClient *dbent.Client, registry *payment.Registry, loadBalancer payment.LoadBalancer, redeemService *RedeemService, subscriptionSvc *SubscriptionService, configService *PaymentConfigService, userRepo UserRepository, groupRepo GroupRepository, affiliateService *AffiliateService) *PaymentService {
+	svc := &PaymentService{entClient: entClient, registry: registry, loadBalancer: newVisibleMethodLoadBalancer(loadBalancer, configService), redeemService: redeemService, subscriptionSvc: subscriptionSvc, configService: configService, userRepo: userRepo, groupRepo: groupRepo, affiliateService: affiliateService}
 	svc.resumeService = psNewPaymentResumeService(configService)
 	return svc
 }
 
-func (s *PaymentService) SetAffiliateService(affiliateService *AffiliateService) {
-	if s == nil {
-		return
-	}
-	s.affiliateService = affiliateService
-}
-
 // --- Provider Registry ---
 
 // EnsureProviders lazily initializes the provider registry on first call.

backend/internal/service/wire.go

@@ -391,53 +391,6 @@ func ProvideSettingService(settingRepo SettingRepository, groupRepo GroupReposit
 	return svc
 }
 
-func ProvideAuthService(
-	entClient *dbent.Client,
-	userRepo UserRepository,
-	redeemRepo RedeemCodeRepository,
-	refreshTokenCache RefreshTokenCache,
-	cfg *config.Config,
-	settingService *SettingService,
-	emailService *EmailService,
-	turnstileService *TurnstileService,
-	emailQueueService *EmailQueueService,
-	promoService *PromoService,
-	defaultSubAssigner DefaultSubscriptionAssigner,
-	affiliateService *AffiliateService,
-) *AuthService {
-	svc := NewAuthService(
-		entClient,
-		userRepo,
-		redeemRepo,
-		refreshTokenCache,
-		cfg,
-		settingService,
-		emailService,
-		turnstileService,
-		emailQueueService,
-		promoService,
-		defaultSubAssigner,
-	)
-	svc.SetAffiliateService(affiliateService)
-	return svc
-}
-
-func ProvidePaymentService(
-	entClient *dbent.Client,
-	registry *payment.Registry,
-	loadBalancer payment.LoadBalancer,
-	redeemService *RedeemService,
-	subscriptionSvc *SubscriptionService,
-	configService *PaymentConfigService,
-	userRepo UserRepository,
-	groupRepo GroupRepository,
-	affiliateService *AffiliateService,
-) *PaymentService {
-	svc := NewPaymentService(entClient, registry, loadBalancer, redeemService, subscriptionSvc, configService, userRepo, groupRepo)
-	svc.SetAffiliateService(affiliateService)
-	return svc
-}
-
 // ProvideBillingCacheService wires BillingCacheService with its RPM dependencies.
 func ProvideBillingCacheService(
 	cache BillingCache,
@@ -454,7 +407,7 @@ func ProvideBillingCacheService(
 // ProviderSet is the Wire provider set for all services
 var ProviderSet = wire.NewSet(
 	// Core services
-	ProvideAuthService,
+	NewAuthService,
 	NewUserService,
 	NewAPIKeyService,
 	ProvideAPIKeyAuthCacheInvalidator,
@@ -535,7 +488,7 @@ var ProviderSet = wire.NewSet(
 	NewModelPricingResolver,
 	NewAffiliateService,
 	ProvidePaymentConfigService,
-	ProvidePaymentService,
+	NewPaymentService,
 	ProvidePaymentOrderExpiryService,
 	ProvideBalanceNotifyService,
 	ProvideChannelMonitorService,